Electrooptical system



Jan. 7, 1930. R. v. L. HARTLEY ELECTRO OPTICAL SYSTEM Filed Dec. 31, 1923 Patented Jan. 7, 1930 UNITED STATES PATENT OFFICE RALPH V. L. HARTLEY, 01' SOUTH ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ELECTROO'PTIGAL SYSTEM Application filed December 31, 1823. Serial No. 683,634.

This invention relates to an electro-optica-l system, and more particularly to a system for indicating electrically transmitted signals by means of a modulated light beam as exempli- 5 fied in systems for the transmission of pictures by electricity.

An object of this invention is to modulate a beam of light in accordance with variations in an electric current.

Crossed light polarizing devices or Nicol prisms with an interposed transparent substance have been used heretofore for this purpose. As is well known, no light will be transmitted through a pair of Nicol prisms providing that the planes of the polarization of the two prisms are at right angles to each other and the interposed transparent substance does not rotate the plane of the polarized light emerging from the first prism. Magnetic means has been used in the past to actuate the transparent body to accomplish rotation of the plane of the polarized light and so to effect transmission of light through the two prisms in varying amounts.

According to this invention, the potential effect of the exciting current on the interposed transparent body causes the rotation of the pla ne of the polarized light. In one embodiment of the invention, a transparent piezo crystal ositioned between two Nicol prisms is electrically excited to control the transmission of light therethrough' The excitation is effected by alternating current modulated in accordance with the successive tone values of the elemental areas of a picture for the transmission of pictures by electricity. The invention is not limited, however. to picture transmission systems, but is applicable to other types of signaling systems. It is also to be understood that the terms used herein, both in the specification and claims, do not limit this invention to the reduction of a picture record at the receiver rom a picture record at the transmitter. The invention is equally applicable to systems, for example,

in which a transitory ima e is produced at the receiver, as in certain forms of television systems.

The term .light as used herein includes not only radiations within the visible spectrum but also radiations having wave lengths above andbelow those of the visible spectrum.

The novel features which are considered characteristic of this invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with other ob ects and advantages thereof, will be further explained in the following description, having reference to the accompanying drawingbwhich shows schematically the invention em odied in a system for the transmission of pictures by electricity. Referring now to the drawing, a sending station A and a receiving station B are connected by transmission line L. At the send 1ng station, a transparent drum 5 mounted on a shaft 6 carries a transparency of the pichire 7 which is to be transmitted. Mounted within the drum 5 is a photo-electric cell'8, the electrical characteristics of which are dependent upon the light intensity within the cell. .Light from a source 9 is focused upon the transparency of the picture 7 by means of lens 10 through an aperture in screen 11. 75 The amount of light which enters the photoelectric cell 8 is determined by the density or tone value of the elemental area of the picture which at any given moment is opposite the aperture in the screen 11: Current flowing through the photo-electric cell 8 is used to modulate carrier waves from a source 12. The modulation is efiected by suitable apparatus indicated by the block 13. As symbolically indicated, this apparatus may consist of electron discharge devices. For details of such apparatus, reference may be made to Patent No. 1,706,032 of M. B. Long, issued March 19, 1929.

At the receiving station B, a receiving drum 15 mounted on a shaft 16 carries a light sensitive record blank 17, such as a film or sensitive paper. Light from a source 18 is focused upon the record blank 17 through an a erture in screen 19 b lenses 20 and 21 a ter passin through t e Nicol prisms 22 and 23 and t e transparent crystal 24. The crystal is provided with electrodes 25, 25. Modulated carrier waves from the line L, after amplification in suitable apparatus indicated by the block 26, are impressed upon the crystal 24. The effect of this current, due to the potential difference between the terminals 25, 25, is to cause the crystal to vibrate at an amplitude proportional to'the voltage of the impressed current. During such vibration, the plane of the polarized light received from prism 22 is rotated so that an amount of light proportional to the amplitude of the vibration of crystal 24, passes through prism 23 to cause the exposure of record blank 17.

The two Nicol prisms and the electrically energized crystal unction as a screen to control the passage of light from the light source 18 to the light record blank 17. The capacity of this screen to pass light therethrough is dependent on .the electro-activity of the crystal.

The drums 5 and 15 may be caused to rotate in synchronism by any suitable means, such for example as that shown in the Long patent supra.

The method of operation consists of transmitting light polarized by a Nicol prism 22 through a transparent body 24 and through an analyzing Nicol prism 23, the two prisms being so ad usted as to extinguish the light when the body 24 is at rest and unstrained. The eflect of a strain in the body 24 is to rotate the plane of polarization of the light with the result that it is no longer extinguished by i the second Nicol prism 23. When a body,

such as a quartz crystal, is made to vibrate at its natural frequency, the strains may be' quite considerable so that an appreciable amount of light is transmitted during each half vibration offthe crystal. One of the difficulties associated with the electrical transmission of pictures is the provision of a satisfactory means for controlling the intensity of the light at the receiving station by the incoming electrical currents The method outlined above furnishes a direct means for accomplishing such control. Where the pictures are to be transmitted by a carrier frequenc over wires or by means of radio, the sending apparatus is so arranged that the amplitude of the high frequency current is varled in accordance with the variations in the intensity of the light controlled by the tone values of successive elemental areas of the picture. Under these conditions, the amplitude of vibration of the crystal varies in a similar manner and, the light passing through the system is accordingly varied. This light, then, fallng upon a 1ght sensitive record blank which is moved in synchronism with the picture, effects the reproduction of the picture.

While this method is particularly adapted to systems emplo ing carrier waves, as use may then be ma e of the resonance of the crystal, 1t is, of course, possible to operate on the same pr nciple in a system where the var ations are transmitted over the line in their original form. More electrical energy will probably be re uired in such a system, as the body 24 will strained by forces of frequencies to which it does not resonate-and to which it offers greater mechanical impedance.

The transmission from station A to station I3 may be effected by radio as well as by wire lme circuits.

While the specific embodiment of the invention shown on the drawing is a system for the transmission of pictures by modulated carrier waves, the scope of the invention is not so limited but is defined by the appended claims. a

What is claimed is:

1. In a signaling system, two terminal stations located at a distance geographically from one another, means at one station for modulating carrier waves in accordance with slgnals, means to transmit said modulated waves from said first station to the other of said stations, receivin means at said other station comprising a 1ght source, a pair of crossed light polarizing devices, means having a natural 1period of vibration and responsive to modu ated waves received from said first station inter sed between said devices for rotating the p ane of polarized light, and means effective under the influence of light passed through said polarizing devices to indicate signals.

2. In a signaling system, two terminal stations located at a distance geographically from one another, means at one station for modulating carrier waves in accordance with signals, means to transmit said modulated waves from said first station to the other of said stations, receivin station comprising a 1ght source, a pair of crossed light polarizing devices, a piezo-electric crystal interposed between said devices, means for exciting said crystal with modu- 'lated waves received from said first station,

and means efi'ective under the influence of light passed through said crystals to indicate signals.

- 3;, In a system for transmitting pictures by electricity, means to produce plcture currents, a source of carrier waves, means to modulate carrier waves from said source with said picture currents, a pair of crossed Nicol prisms,.a source of light, a transparent piezoelectric crystal located between said risms, means to e cite a y al with In elated means at said other Ill carrier waves to rotate the plane of the polarized light incident upon said crystal, and means eflective under the influence of light passed through said polarizing devices to re-' from said source, means to excite said crystal with modulated carrier waves to rotate the plane of the polarized light incident upon said crystal, and means 'eflective under the. influence of light passed through sald polarizing devices to reproduce the picture.

5. In a system for transmitting pictures by electricity, a transparency of the picture to be transmitted, scanning means comprising a rotating cylinder upon which the transparency of the picture is mounted, a photoelectric cell within said cylinder for producing picture currents, a source of carrier wayes, means comprising electron discharge devices for modulating carrier waves from said source with picture currents from said photoelectric cell, a light polarizing device, a p1ezo: electric crystal having a natural period of vibration equal to the frequency of the carrier waves from said source, means to excite said crystal with modulated carrier waves to rotate the plane of the polarized light lncident upon said crystal, and means efiectlve under the influence of light passed through said polarizing device to reproduce the picture.

6. A signal receiving system comprising transparent crystalline material capable of rotating the plane of polarized light passed therethrough when variably stralned, and means associated therewith and controlled by carrier current modulated by signaling current incoming from a geographlcally distant station to maintain said crystalline material in vibration at its own natural frequency.

7. In a system for the transmission of signals from one station to another, located at a distance geographically therefrom, means at the sending station to modulate a carrier current in accordance with signals, means to transmit said modulated current to the re ceiving station, a source of light at the receiving station, a recording device acted upon by said source of light, and a light valve comprising a vibrating member responsive directly to the incoming modulated carrier current to vary the amount of light passed to said recording device.

8. In a system for transmitting pictures by electricity, means to produce picture currents, a source of carrier waves, means to modulate carrier waves from said source with said picture currents, a pair of crossed Nicol prisms, a source of light, transparent crystalline material which is capable of rotating the plane of polarized light passed therethrough when variably strained, located in a light path between said prisms, means to variably strain said material with modulated carrier waves to rotate the plane of the polarized light incident upon said material, and means eflt'ective under the influence of light passed through said polarizing devices to reproduce the picture.

9. In a system for transmitting pictures by electricity, means to produce picture currents, a source of carrier waves, means to modulate carrier waves from said source with said picture currents, a pair of crossed Nicol prisms, a source of light, transparent crystalline material having a natural period of vibration equal to the frequency of the carrier waves from said source and capable of'rotating the plane of polarized light passed therethrough when variably strained, means to excite said crystalline material with modulated carrier waves to rotate the plane of the polarized light incident upon said material, and means effective under the influence of light passed through said polarizing devices to reproduce the picture. I

10. A picture receiving system comprising transparent crystalline materiai capable of rotating the plane of polarized light passed therethrough when variably strained, means associated therewith and controlled by carrier current modulated by picture current to maintain said crystalline material in vibration at its own natural frequency, and means for producing a picture in accordance with the light passed through said material.

11. In a system for transmitting pictures electrically, means to produce picture currents, a source of carrier waves, means to modulate carrier waves from said source with said picture currents, a source of light, a light valve comprising a vibration member upon which the modulated carrier waves are impressed to vary the amount of light passed by said valve, and means effective under the influence of the light passed by said valve to produce the picture.

1 12. In a system for transmitting pictures electrically, a source of picture modulated carrier current, a source of light, a light valve comprising a vibration member upon which modulated carrier current from said source is impressed to vary the amount of light passed by said valve, and means efiec-tive under the influence of the light passed by said valve to produce the picture.

In witness whereof, I hereunto subscribe my name this 28th day of December A. D., 1923.

RALPH V. L. HARTLEY. 

